Lysosomal Acid Lipase (LAL) Deficiency is a rare lysosomal storage disease (LSD) characterized by a failure to breakdown cholesteryl esters (CE) and triglycerides (TAG) in lysosomes due to a deficiency of the enzyme. LAL deficiency resembles other lysosomal storage disorders with the accumulation of substrate in a number of tissues and cell types. In LAL deficiency substrate accumulation is most marked in cells of the reticuloendothelial system including Kupffer cells in the liver, histiocytes in the spleen and in the lamina propria of the small intestine. Reticuloendothelial cells express the macrophage mannose/N-acetyl glucosamine receptor (also known as macrophage mannose receptor, MMR, or CD206), which mediates binding, cell uptake and lysosomal internalization of proteins with GlcNAc or mannose terminated N-glycans, and provides a pathway for the potential correction of the enzyme deficiency in these key cell types.
LAL Deficiency is a multi-system disease that most commonly manifests with gastrointestinal, liver and cardiovascular complications and is associated with significant morbidity and mortality. The clinical effects of LAL deficiency are due to a massive accumulation of lipid material in the lysosomes in a number of tissues and a profound disturbance in cholesterol and lipid homeostatic mechanisms, including substantial increases in hepatic cholesterol synthesis. LAL deficiency presents as at least two phenotypes: Wolman Disease (WD) and Cholesteryl Ester Storage Disease (CESD).
Wolman Disease, named after the physician who first described it, is the most aggressive presentation of LAL deficiency. This phenotype is characterized by gastrointestinal and hepatic manifestations including growth failure, malabsorption, steatorrhea, profound weight loss, lymphadenopathy, splenomegaly, and hepatomegaly. Wolman Disease is rapidly progressive and invariably fatal usually within the first year of life. Case report review indicates that survival beyond 12 months of age is extremely rare for patients who present with growth failure due to severe LAL deficiency in the first year of life. In this most aggressive form, growth failure is the predominant clinical feature and is a key contributor to the early mortality. Hepatic involvement as evidenced by liver enlargement and elevation of transaminases is also common in infants.
The diagnosis of Wolman Disease is established through both physical findings and laboratory analyses. Infants are typically hospitalized within the first two months of life due to diarrhea, persistent vomiting, feeding difficulty, stunted growth, and failure to thrive. Physical findings include abdominal distention with hepatomegaly and splenomegaly, and radiographic examination often reveals calcification of the adrenal glands. Laboratory evaluations typically reveal elevated levels of serum transaminases and absent or markedly reduced endogenous LAL enzyme activity. Elevated blood levels of cholesterol and triglycerides are seen in some patients.
Patients with LAL deficiency can also present later in life with predominant liver and cardiovascular involvement, and this is often called Cholesteryl Ester Storage Disease (CESD). In CESD, the liver is severely affected with marked hepatomegaly, hepatocyte necrosis, elevation of transaminases, cirrhosis, and liver fibrosis. Due to increased levels of CE and TAG, the cardiovascular involvement can be characterized by hyperlipidemia. An accumulation of fatty deposits on the artery walls (atherosclerosis) has been reported in some subjects suffering from CESD. The deposits narrow the arterial lumen and can lead to vessel occlusion increasing the risk of significant cardiovascular events including myocardial infarction and strokes. However, not all subjects suffering from LAL deficiency develop atherosclerosis. For example, Wolman Disease patients are overwhelmed with other symptoms associated with the disease, including enlarged liver and spleen, lymphadenopathy, and the malabsorption by the small intestine, but WD is not generally characterized by atherosclerosis (The Metabolic and Molecular Bases of Inherited Disease (Scriver, C. R., Beaudet, A. L., Sly, W. S. and Valle D., eds) 7th ed., Volume 2 p. 2570 McGraw-Hill, 1995). Likewise, not all CESD patients exhibit atherosclerosis See, Di Bisceglie et al., Hepatology 11: 764-772 (1990), Ameis et al., J. Lipid Res. 36: 241-250 (1995). The presentation of CESD is highly variable with some patients going undiagnosed until complications manifest in late adulthood, while others can have liver dysfunction presenting in early childhood. CESD is associated with shortened lifespan and significant ill health. The life expectancy of those with CESD depends on the severity of the associated complications.
Current treatment options for Wolman Disease are very limited. Antibiotics are administered to infants with pyrexia and/or evidence of infection. Steroid replacement therapy for adrenal insufficiency and specialized nutritional support may be prescribed, and while there is no evidence that these interventions prevent death, it is also unclear at present if they have an impact on short term survival. In a series of four patients with LAL deficiency treated with bone marrow transplantation, all four patients died due to complications of the procedure within months of transplantation. Although some success has been described in subsequent case reports, the mortality rate remains high and many patients are not transplanted as they are too ill to survive the pre-transplant conditioning regime. The very small number of reported long-term survivors does indicate that correction of enzyme deficiency in hemopoietic cells alone is sufficient to substantially improve the clinical status in this disease. Typically clinical support is provided through dietary restrictions in an attempt to restrict the build-up of nontransportable and noncatabolizable lipids associated with the acute manifestations of the disease leading to death.
Current treatment options for the CESD phenotype are focused at symptomatic treatment via control of lipid accumulation through diet that excludes foods rich in cholesterol and triglycerides and suppression of cholesterol synthesis and apolipoprotein B production through administration of cholesterol lowering drugs (e.g., statins and cholestyramine). Although some clinical improvement may be seen, the underlying disease manifestations persist and disease progression still occurs.
It has been suggested that enzyme replacement therapy with recombinant LAL may be a viable treatment option for lysosomal acid lipase deficiency and related conditions (see, Meyers et al. (1985) Nutrition Res. 5(4):423-442; WO9811206; and Besley (1984) Clinical Genetics 26:195-203). Some studies using a mouse model of LAL deficiency have demonstrated correction of some abnormalities of LAL deficient (LAL−/−) mice through infusion of high doses (more than 1 milligram per kilogram of body weight) of recombinant human LAL once every 3 days (see, for example, Grabowski US 2007/0264249). These earlier studies to correct the defects within LAL deficient mice suggested that relatively high amounts and frequent dosages of recombinant LAL protein were required in order to correct the underlying phenotypes. It is also important to note that, unlike the LAL−/− rat model described initially by Yoshida and Kuriyama (1990) Laboratory Animal Science, vol 40, p 486-489, the LAL−/− mice model used in the above study does not closely resemble human WD in that the LAL deficient mice do not exhibit growth defects that are seen in human patients.
To date, no exogenous LAL has been administered to humans and there is no effective therapy available for treating LAL deficiencies including WD, CESD, and others. Therefore, there is a dire need for therapies with a minimized frequency of administration in order to improve the quality of life for patients. Further, therapeutically effective doses that restore growth, normalize liver function, increase LAL tissue concentrations, and increase LAL activity in human patients are desirable.